1. Field of the Invention
The present invention relates generally to optical systems and more particularly to light-processing apertures in optical systems.
2. Description of the Related Art
Optical components, e.g., lenses and mirrors, typically have limited component apertures over which their optical processes are valid. In optical systems, these component apertures are often modified by the insertion of a discrete aperture which further limits the area of the optical process to improve a system performance parameter, e.g., reduce spherical aberration or select the depth of focus.
A discrete aperture's use in an optical system is often enhanced if the aperture's opening can be adjusted to accommodate changing conditions or system requirements. Accordingly, aperture structures have been developed in which the area of the aperture's opening is selectively adjusted by various methods, e.g., mechanical and electromechanical. Although the area of these apertures can be selected, there is typically no control over the attenuation of the aperture, i.e., the open area of the aperture is fully transmissive. Accordingly, the processing functions of conventional apertures is generally limited to restriction of an incident light beam. In addition, conventional adjustable apertures typically include moving parts which reduce their reliability and speed.
In contrast, electro-optical components are available which can process incident light with a plurality of attenuation values. For example, a polarizer and a black guest host liquid crystal can function as an electrically-responsive attenuator as can also a twisted nematic liquid crystal which is positioned between a pair of polarizers. Although these components can selectively attenuate a light beam, they lack the ability to provide spatially different attenuations over the cross section of a light beam.